GLSL 编程/GLUT/双面平滑曲面
本教程涵盖双面逐像素光照（即双面 Phong 着色）。
在这里，我们将平滑镜面高光教程中讨论的逐像素光照与双面曲面教程中讨论的双面光照结合起来。
对平滑镜面高光教程代码的必要更改是：背面材料的新属性，片段着色器中材料参数的新局部变量，这些变量根据gl_FrontFacing设置为正面材料参数或背面材料参数。此外，如果渲染背面，则表面法线向量将被取反。此外，背面剔除必须像透明度教程中描述的那样被禁用。实际上这非常简单。
顶点着色器可能看起来像这样
attribute vec4 v_coord;
attribute vec3 v_normal;
varying vec4 position; // position of the vertex (and fragment) in world space
varying vec3 varyingNormalDirection; // surface normal vector in world space
uniform mat4 m, v, p;
uniform mat3 m_3x3_inv_transp;
void main()
{
position = m * v_coord;
varyingNormalDirection = normalize(m_3x3_inv_transp * v_normal);
mat4 mvp = p*v*m;
gl_Position = mvp * v_coord;
}
而片段着色器可能是
varying vec4 position; // position of the vertex (and fragment) in world space
varying vec3 varyingNormalDirection; // surface normal vector in world space
uniform mat4 m, v, p;
uniform mat4 v_inv;
struct lightSource
{
vec4 position;
vec4 diffuse;
vec4 specular;
float constantAttenuation, linearAttenuation, quadraticAttenuation;
float spotCutoff, spotExponent;
vec3 spotDirection;
};
lightSource light0 = lightSource(
vec4(0.0, 1.0, 2.0, 1.0),
vec4(1.0, 1.0, 1.0, 1.0),
vec4(1.0, 1.0, 1.0, 1.0),
0.0, 1.0, 0.0,
180.0, 0.0,
vec3(0.0, 0.0, 0.0)
);
vec4 scene_ambient = vec4(0.2, 0.2, 0.2, 1.0);
struct material
{
vec4 ambient;
vec4 diffuse;
vec4 specular;
float shininess;
};
material frontMaterial = material(
vec4(0.2, 0.2, 0.2, 1.0),
vec4(1.0, 0.0, 0.0, 1.0),
vec4(1.0, 1.0, 1.0, 1.0),
100.0
);
material backMaterial = material(
vec4(0.2, 0.2, 0.2, 1.0),
vec4(0.0, 0.0, 1.0, 1.0),
vec4(1.0, 1.0, 1.0, 1.0),
100.0
);
void main()
{
vec3 normalDirection = normalize(varyingNormalDirection);
vec4 ambientColor;
vec4 diffuseColor;
vec4 specularColor;
float shininess;
if (gl_FrontFacing)
{
ambientColor = frontMaterial.ambient;
diffuseColor = frontMaterial.diffuse;
specularColor = frontMaterial.specular;
shininess = frontMaterial.shininess;
}
else
{
ambientColor = backMaterial.ambient;
diffuseColor = backMaterial.diffuse;
specularColor = backMaterial.specular;
shininess = backMaterial.shininess;
normalDirection = -normalDirection;
}
vec3 viewDirection = normalize(vec3(v_inv * vec4(0.0, 0.0, 0.0, 1.0) - position));
vec3 lightDirection;
float attenuation;
if (0.0 == light0.position.w) // directional light?
{
attenuation = 1.0; // no attenuation
lightDirection = normalize(vec3(light0.position));
}
else // point light or spotlight (or other kind of light)
{
vec3 positionToLightSource = vec3(light0.position - position);
float distance = length(positionToLightSource);
lightDirection = normalize(positionToLightSource);
attenuation = 1.0 / (light0.constantAttenuation
+ light0.linearAttenuation * distance
+ light0.quadraticAttenuation * distance * distance);
if (light0.spotCutoff <= 90.0) // spotlight?
{
float clampedCosine = max(0.0, dot(-lightDirection, light0.spotDirection));
if (clampedCosine < cos(radians(light0.spotCutoff))) // outside of spotlight cone?
{
attenuation = 0.0;
}
else
{
attenuation = attenuation * pow(clampedCosine, light0.spotExponent);
}
}
}
vec3 ambientLighting = vec3(scene_ambient) * vec3(ambientColor);
vec3 diffuseReflection = attenuation
* vec3(light0.diffuse) * vec3(diffuseColor)
* max(0.0, dot(normalDirection, lightDirection));
vec3 specularReflection;
if (dot(normalDirection, lightDirection) < 0.0) // light source on the wrong side?
{
specularReflection = vec3(0.0, 0.0, 0.0); // no specular reflection
}
else // light source on the right side
{
specularReflection = attenuation * vec3(light0.specular) * vec3(specularColor)
* pow(max(0.0, dot(reflect(-lightDirection, normalDirection), viewDirection)), shininess);
}
gl_FragColor = vec4(ambientLighting + diffuseReflection + specularReflection, 1.0);
}
恭喜您完成了本简短教程。我们已经看到了
- 如何使用逐像素光照渲染双面曲面。
如果您还想了解更多
除非另有说明，否则本页上的所有示例源代码均已授予公有领域。
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